with语句

try:
    with open('data.txt') as f #等价于f = open('data.txt','w') 
        for each_line in f:
            print(each_line)
        
except OSError as reason: #使用异常处理执行到这一步时边不会再执行后面的语句，因此常常是f.close()不能执行而出问题，上面的with语句可以有效解决该问题
    print('出错啦'+str(reason))

使用with语句可以处理多个项目用 ‘，’隔开，例如

with A() as a:

　　with B() as b:

　　　　suite

可以写成：

with A() as a, B() as b:
　　suite